Semiconductor devices and liquid crystal display devices are produced by the so-called photolithography technique in which a pattern formed on a mask is transferred onto a photosensitive substrate. The exposure apparatus, which is used in the photolithography step, includes a mask stage for supporting the mask and a substrate stage for supporting the substrate. The pattern on the mask is transferred onto the substrate via a projection optical system while successively moving the mask stage and the substrate stage. In recent years, it is demanded to realize the higher resolution of the projection optical system in order to respond to the further advance of the higher integration of the device pattern. As the exposure wavelength to be used is shorter, the resolution of the projection optical system becomes higher. As the numerical aperture of the projection optical system is larger, the resolution of the projection optical system becomes higher. Therefore, the exposure wavelength, which is used for the exposure apparatus, is shortened year by year, and the numerical aperture of the projection optical system is increased as well. The exposure wavelength, which is dominantly used at present, is 248 nm of the KrF excimer laser. However, the exposure wavelength of 193 nm of the ArF excimer laser, which is shorter than the above, is also practically used in some situations. When the exposure is performed, the depth of focus (DOF) is also important in the same manner as the resolution. The resolution R and the depth of focus δ are represented by the following expressions respectively.R=k1·λ/NA  (1)δ=±k2·λ/NA2  (2)
In the expressions, λ represents the exposure wavelength, NA represents the numerical aperture of the projection optical system, and k1 and k2 represent the process coefficients. According to the expressions (1) and (2), the following fact is appreciated. That is, when the exposure wavelength λ is shortened and the numerical aperture NA is increased in order to enhance the resolution R, then the depth of focus δ is narrowed.
If the depth of focus δ is too narrowed, it is difficult to match the substrate surface with respect to the image plane of the projection optical system. It is feared that the focus margin is insufficient during the exposure operation. In view of the above, the liquid immersion method has been suggested, which is disclosed, for example, in International Publication No. 99/49504 as a method for substantially shortening the exposure wavelength and widening the depth of focus. In this liquid immersion method, the space between the lower surface of the projection optical system and a surface of the substrate is filled with a liquid such as water or any organic solvent to form a liquid immersion area so that the resolution is improved and the depth of focus is magnified about n times by utilizing the fact that the wavelength of the exposure light beam in the liquid is 1/n as compared with that in the air (n represents the refractive index of the liquid, which is about 1.2 to 1.6 in ordinary cases).
As shown in FIG. 18, when the substrate P is subjected to the liquid immersion exposure, a situation arises such that a part or all of the liquid immersion area AR2′ which covers the projection area AR1′ of the projection optical system is formed outside the substrate P. In such a situation, the upper surface of the substrate stage PST′ at a portion thereof around the substrate P makes contact with the liquid. Therefore, the member (or any coating thereof), which forms the upper surface of the substrate stage PST′, is easily deteriorated and/or damaged. When the deterioration and/or the damage is caused as described above, an inconvenience arises such that the rate of operation of the exposure apparatus is lowered due to the execution of the maintenance operation such as the repair and/or the exchange of the substrate stage PST′.
When the edge area of the substrate P is subjected to the exposure in a state in which a part of the liquid immersion area AR2′ is formed outside the substrate P, the following possibility may arise. That is, the liquid flows from the upper surface to a side of the back surface of the substrate through a gap (space or interstice) between the substrate and the substrate stage, and the liquid inflows into the space between the substrate and the substrate stage (substrate holder). In such a situation, a possibility arises such that the substrate stage cannot hold or retain the substrate satisfactorily. For example, the liquid, which has inflowed into the space between the back surface of the substrate and the substrate stage, behaves as a foreign matter. Therefore, there is such a possibility that the flatness of the supported substrate may be consequently deteriorated. In other situations, it is also conceived that any adhesion trace (so-called water mark) may be formed due to the vaporization of the inflowed liquid. The water mark also functions as a foreign matter. Therefore, there is such a possibility that the flatness of the supported substrate may be consequently deteriorated. Further, for example, there is also such a possibility that the following inconvenience may arise. That is, the substrate stage is thermally deformed due the heat of vaporization brought about upon the vaporization of the liquid inflowed into the space between the substrate and the substrate stage.